Surprisingly, up until a year ago, [Jimmy] hadn’t seen a Nixie tube. Awful we know, but he has come around to the beauty of glowing numbers in a tube. He recently found an old millivolt meter in a junk pile that used Nixie tubes. The wondrous orange glow beckoned him, so [Jimmy] decided to build a clock.
Just about all of the Nixie clocks we’ve seen (including non-clock builds) rely on building a controller for the Nixie tubes. The controllers range from Nixie Arduino shields to the good ‘ol 74141 IC. [Jimmy] realized he didn’t need to bother with controlling the tubes in an already functional millivolt meter – he only needed to send the right voltage.
For his clock build, [Jimmy] used an Arduino to output a voltage through a bunch of resistor dividers. For example, if the time is 12:30, the output voltage will be 12.30mV. Using this technique, the values for the needed resistors don’t exist, so a little bit of PWM means the Arduino keeps fairly good time.
There’s one added bonus of [Jimmy]’s clock – because the voltage varies around 0.01mV, the finished project acts like a digital version of Lord Vetinari’s clock. It may not be perfect, but at least a nice piece of equipment was saved from the trash.